1. Field of the Invention
This invention is directed to a method and apparatus for detecting the location, velocity, size and type of particles in a weather system. More particularly, the invention relates to detecting particles in a weather system with a wide-angle multiple-Doppler radar network using a single transmitting antenna and at least one passive receiving antenna with a wide angle view.
2. Description of Prior Art
A conventional Doppler radar station is a monostatic station meaning the transmitting antenna is also the receiving antenna. Such a station may focus a beam of transmitted electromagnetic radiation on water particles in a cloud, and from the Doppler shift in echoes from the particles determine the component of velocity of the particles in the direction of the beam. In effect, the single radar station can detect the velocity of particles, and thus the wind, along a radial line from the radar station.
Bistatic and polystatic radar networks have been used in the past to detect the velocity of aircraft, missiles, etc. In a bistatic radar system, the transmitting and receiving antennas are separated. In a polystatic radar system, there are multiple receiving antennas for each transmitting antenna. The receiving antennas are focussed as a group as a narrow beam antenna monitoring the object illuminated by the transmitting beam. Exemplary of a polystatic radar system is the system taught in U.S. Pat. No. 4,994,809, entitled "Polystatic Correlating Radar." This radar system has no particular utility as a weather radar system.
The concept of using a multi-static radar system to detect wind velocity is briefly discussed in an article entitled "Measuring Winds With Pulsed C-Band Radar" in NASA Technical Briefs, October 1989. The article proposes to use multiple receiving stations; i.e., a polystatic system to get velocity vectors in multiple directions so as to determine the actual velocity of particles and, thus, the wind. This system uses a narrow beam receiving station. Accordingly, the receiving station would detect wind velocity at one point in the sky; i.e., the intersection of the transmitted beam and the focussed beam of the receiving station. To obtain any useful data, the receiving antenna would have to scan some length of the transmitted beam, the transmitted beam would have to be indexed and the receiving beam would have to again scan the transmitted beam. The problem with such a system is that obtaining wind velocity for more than one point in the sky requires either hundreds of antennas focussed on different parts of the transmitted beam or some system for rapid-coordinated scanning by multiple antennas. This would be an extremely expensive system if it could even operate quickly enough to obtain useful data for different portions of the sky.